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Math Help - Cost

  1. #1
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    Urgent Please Help Cost

    1. The following function represents the cots in hundreds of dollars for producing pens, where x represents 1000's of units
    c(x)=.4x^2-16x+200 , 25 ≤ x ≤ 40

    a) Estimate the cost for making the 36th 1000-unit run using the marginal cost function derivative.

    b) Find the actual cost for making the 36th 1000-unit run.

    c) Find the percent margin of error for your cost estimate in part a.
    Last edited by Hallah_az; April 8th 2006 at 08:17 PM. Reason: Only part of the question was submitted, sending again
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  2. #2
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    Quote Originally Posted by Hallah_az
    Please explain:
    2. Find the equation of the line tangent to f(x)=1/x at the point x=1
    You need to find the derivative.
    Thus, you have f(x)=\frac{1}{x}=x^{-1}
    Its derivative is the power rule, thus,
    f'(x)=(-1)x^{-1-1}=-x^{-2}=-\frac{1}{x^2}
    At, point x=1 we have, y=\frac{1}{1}=1.
    Now we use the point-intercept formula. Which says that if a line passes through point (x_0,y_0) and has slope m then, its equation is,
    y-y_0=m(x-x_0). Thus, in this case we have the point, which is (1,1). Now we need the slope. That is the derivative evaluated at that point which is f'(1)=-\frac{1}{1^2}=-1 the equation is,
    y-1=-1(x-1)
    Thus,
    y-1=-x+1
    Thus,
    y=-x+2
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  3. #3
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    Thank you!

    I got the 2nd part, but I do not understand a) the marginal cost function; b) actual cost; c) the percent margin

    Could you please explain. Thank you for all your help!
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